Field of the Invention
The present invention relates to a method and apparatus for simple identification and signature.
Creating unforgeable ID cards based on the emerging technology of smart cards is an important problem with numerous commercial and military applications. The problem becomes particularly challenging when two parties (the prover A and the verifier B) are adversaries, and one wants to make it impossible for B to misrepresent himself as A even after he witnesses and verifies arbitrarily many proofs of identity generated by A. Typical applications includes passports (which are often inspected and photocopied by hostile governments), credit cards (whose numbers can be copied by blank cards or used over the phone), computer passwords (which are vulnerable to hackers and wire tappers) and military command and control systems (whose terminals may fall into enemy hands). Three levels of protection may be distinguished between:
(1) Authentication: A can prove to B that he is A, but someone else cannot prove to B that he is A.
(2) Identification: A can prove to B that he is A, but B cannot prove to someone else that he is A.
(3) Signature: A can prove to B that he is A, but B cannot prove even to himself that he is A.
Authentication is useful only against external threats when A and B cooperate. The distinction between identification and signature is subtle, and manifests itself mainly when the proof is interactive and the verifier later wants to prove its existence to a judge. In identification, B can create a credible transcript of an imaginary communication by carefully choosing both the questions and the answers in the dialog, while in signature only real communication with A could generate a credible transcript. However, in many commercial and military applications the main problem is to detect forgeries in real time and to deny the service, access or response that the forger wants. In these cases the transcript and judge are irrelevant, and identification and signature requirements can be used interchangeably.